Positioning a print inside a frame is a big part of framing a print.
Framing a print is not an exact science but does take a little understanding.
Why make an 8x12 print instead of an 8x10? Your 8x10 is literally 'inside' the 8x12!
So, why not just cut (crop) your print to 8x10? Sometimes the 8x12 is a better option since it lets you decide what to see in your frame. Or, possibly you liked the content of the entire image and were reluctant to crop it.
You can crop the print where you think it looks best if you wish. But there is often no need. I'll explain.
Your first choice in framing your print is whether to use a mat. Generally a mat adds artistic impact to an important image.
You can easily find a wide variety of inexpensive standard frame and mat sizes at craft stores like Michaels, Franks, and others. Frames can be found with mats already inside; and frames and mats can be found separately.
A very common size of frame and mat is an 11x14 frame; with an 11x14 mat that has an 8x10 opening.
Position your print under the mat where you like. We'll try the same print from above.
Or maybe you would like a different look?
If you don't want to use a mat, it's still not a problem. Just find an 8x10 frame and cut your print to about 8x11 with a pair of sharp scissors. There is no need to cut it all the way down exactly to 8x10 inches since the frame will hide a little of the extra edge. So don't make it too small. Then position your print inside your fame.
There are other options, too. 8x12 frames are available. You could even have one made.
This does not explain how to mount your print or how to put it in a frame or under a mat. Mounting your print is an important aspect of framing and will need to be done by someone who has knowledge on the subject.